1. Field of the Invention
The invention relates generally to drill bits, and, in particular, to systems for retaining hydraulic nozzles in drill bits.
2. Description of the Prior Art
Regardless of whether a drill bit is a roller cone bit or drag bit, drilling mud or hydraulic fluid is provided as part of the bit design for the purposes of cooling and cleaning the bit. It has been long known that the functions of the hydraulic subsystem within a drill string can be materially assisted by providing nozzle passages for the hydraulic mud from the interior of the drill bit to form a jet flow toward the point where the cutters engage the bottom of the hole. The drilling mud, however, is extremely abrasive and is supplied under high pressure. As a result, hydraulic nozzles are subject to a highly erosive jet stream. Even though the nozzles are made of tungsten carbide or other hardened metals, they must be frequently replaced, inasmuch as the nozzles will erode, in many cases long before the drill bit becomes worn.
Some bits have nozzles that are permanently fixed into place either by molding, brazing or welding. The prior art has also developed replaceable nozzles. Typically, such replaceable nozzles are retained in the bit against the high hydraulic pressure by various combinations of snap rings and grooves. Because of the high pressure and erosive nature of the drilling mud, replaceable nozzles retained by a combination of a snap ring disposed in a groove defined in the bit body have typically been susceptible to nozzle loss. This has typically resulted either because the portion of the bit body adjacent to the snap ring groove has been washed away or because portions of the nozzle body and snap ring have been eroded.
Because of the unsuitability of snap ring replaceable nozzles, various other types of replaceable nozzles have been devised in the prior art which either place the snap ring away from a position where it can erode or provide an end-cap which threads into the bit body to retain the nozzle. Alternatively, the nozzle itself may be threaded directly into the bit body. One such example is found in a tungsten carbide molded nozzle which is described in U.S. Pat. No. 4,567,954, assigned to the same assignee as the present invention. Other prior art examples of threaded nozzles are shown and discussed, for example, in Radtke, "Drill Bit Nozzle", U.S. Pat. No. 4,381,825.
Examples of threaded nozzles which incorporate a retaining ring can also be found in Thomas, "Nozzle Retention Method for Rock Bit", U.S. Pat. No. 4,407,378, which shows a resilient nozzle having a plurality of radially circumferential fins which are jammed in the nozzle bore defined in the bit body.
Another example of a threadless nozzle not incorporating a retaining ring is shown by Goolsbee, "Quick Change Slush Nozzle", U.S. Pat. No. 2,520,362, wherein a multiple part nozzle is formed into two telescopic shapes which wedge together and are retained in place by the last boot.
Long tubular nozzles having an expanded internal end-flange, which is mounted in a mating indentation in the interior of the bit body, can be found in Mori, "Retrievable Jet Bit with Swing Jets", U.S. Pat. No. 3,393,756.
Threaded nozzles are not satisfactory for several reasons. The threads for the nozzles are difficult to form in certain types of bit construction. Additionally, the nozzles are relatively difficult, if not impossible, to replace, due to the substantial erosion and other damage which the threads typically receive in the drilling environment.
What is needed is a simple, rugged, system for a threadless replaceable nozzle which is not subject to erosion of the nozzle retaining system, and which allows simple and quick insertion and replacement of the nozzle.